1. Field of the Invention
This invention relates to a liquid injection recording head for injecting liquid and forming flying droplets to thereby accomplish recording.
2. Description of the Prior Art
Ink jet recording methods (liquid injection recording methods) have recently attracted attention in that the noise produced during recording is negligibly small and that it is capable of accomplishing high-speed recording and moreover accomplishing recording without requiring the special processing such as fixation of images on so-called plain paper.
Among these methods, the liquid injection recording methods disclosed, for example, in Japanese Laid-open Patent Application No. 51837/1979 and German Laid-open Patent Application (DOLS) No. 284,3064 have a feature different from the feature of the other liquid injection recording methods in that heat energy is caused to act on liquid to thereby obtain a motive force for droplet discharge.
That is, according to the recording methods disclosed in the aforementioned publications, the liquid subjected to the action of heat energy causes a state change resulting in a sharp increase in volume and by the action force based on the state change, liquid is discharged from the orifices at the fore end of the recording head unit, whereby flying droplets are formed and adhere to a recording medium, thus accomplishing recording.
Particularly, the liquid injection recording method disclosed in DOLS No. 284,3064 is not only very effectively applicable to the so-called drop-on demand recording method, but also can easily embody a recording head having its recording head unit of the full line type provided with highly dense multiorifice and therefore has a feature that images of high resolution and high quality can be obtained at a high speed.
The recording head unit of the apparatus applied to the above-described recording method is provided with a liquid discharging portion having orifices provided to discharge liquid therefrom and liquid flow paths communicating with said orifices and having as a part of the construction thereof a heat-acting portion in which the heat energy for discharging droplets acts on the liquid, and an electro-thermal converting member as means for generating the heat energy.
The electro-thermal converting member is provided with a pair of electrodes provided on a support member, and a heat generation resistive layer connected to these electrodes and having an area for generating heat (a heat generating portion) between these electrodes.
A typical example of the structure of such a liquid injection recording head is shown in FIGS. 1A and 1B of the accompanying drawings. FIG. 1A is a fragmentary front view of the liquid injection recording head as seen from the orifice side, and FIG. 1B is a fragmentary cross-sectional view taken along the dot-and-dash line XY of FIG. 1A.
The recording head 101 is of a structure in which the surface of a base plate 102 having an electro-thermal converting member on the surface thereof is joined so as to be covered with a grooved plate 103 provided with a predetermined number of grooves having a predetermined width and depth at predetermined line density, whereby orifices 104 and a liquid discharging portion 105 are formed. In the case of the recording head shown in FIG. 1, there is provided a plurality of orifices 104, whereas the present invention is not restricted to such a recording head, but a recording head having a single orifice also falls within the category of the present invention.
The liquid discharging portion 105 has orifices 104 for discharging liquid at the terminal end thereof, and a heat-acting portion 106 which is a portion in which the heat energy generated by the electro-thermal converting member acts on the liquid to produce bubbles and causes a sharp state change caused by the expansion and contraction of the volume thereof.
The heat-acting portion 106 overlies the heat generating portion 107 of the electro-thermal converting member and the bottom surface thereof provides a heat-acting surface 108 as the surface of the heat generating portion 107 which contacts the liquid.
The heat generating portion 107 is comprised of a lower layer 109 provided on a support member 114, a heat generation resistive layer 110 provided on the lower layer 109, and an upper layer 111 provided on the heat generation resistive layer 110. Electrodes 112 and 113 for supplying an electric power to the heat generation resistive layer 110 to generate heat are provided on the surface of the heat generation resistive layer 110. The electrode 112 is an electrode common to the heat generating portions of the liquid discharging portions, and the electrode 113 is a selection electrode for selecting the heat generating portions of the liquid discharging portions and causing them to generate heat and is provided along the liquid flow paths of the liquid discharging portions.
The upper layer 111 in the heat generating portion 107 isolates the heat generation resistive layer 110 from the liquid filling the liquid flow path of the liquid discharging portion 105 to chemically and physically protect the heat generation resistive layer 110 from the liquid used and also prevents the electrodes 112 and 113 from being short-circuited through the liquid. The upper layer 111 also serves to prevent any electrical leak between the adjacent electrodes. Especially, the prevention of the electrical leak between the selection electrodes or the prevention of the electric erosion of the electrodes which may result from the electrodes below the liquid flow paths contacting the liquid for some reason or other and supplying an electric power to the liquid is important and, for this purpose, the upper layer 111 having such a protective function is provided on at least the electrode underlying the liquid flow path.
Further, the liquid flow path provided in each liquid discharging portion communicates, upstream thereof, with a common liquid chamber (not shown) for storing therein the liquid to be supplied to said liquid flow path, but usually, the electrode connected to the electro-thermal converting member provided in each liquid discharging portion is provided so as to pass below said common liquid chamber upstream of the heat-acting portion because of the convenience of the designing thereof. Accordingly, said upper layer is usually provided to prevent the electrode from contacting the liquid in this portion as well.
The base plate 102 is provided with the support member 114 formed of silicon, glass, ceramics or the like, the lower layer 109 formed of a metal oxide such as SiO.sub.2, zirconium oxide, tantalum oxide or magnesium oxide on the support member 114, the heat generation resistive layer 110, the common electrode 112 and the selection electrode 113 on the opposite sides of the heat generation resistive layer, the portion of the heat generation resistive layer 110 which is not covered with the electrodes, and the upper layer 111 provided so as to cover the electrodes 112 and 113.
As described above, in the conventional base plate, various layers are formed on a rigid support member by a method such as sputtering or evaporation. This is not suitable for mass production and has required a number of steps of process and a long time for manufacture. Also, the materials are expensive and therefore the cost of the liquid injection recording head has unavoidably been high. Further, the manufactured base plate is rigid and this has limited the range of use of the liquid injection recording head.